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CALCAREOUS NANNOPLANKTON BIOSTRATIGRAPHY FROM THE EARLY/MIDDLE MIOCENE BOUNDARY (KARPATIAN - BADENIAN BOUNDARY) IN THE STYRIAN AND VIENNA BASIN

Stjepan Coric
Instiute of Paleontology, UNI-Wien, Althanstrasse 14, 1090 Vienna, stjepan.coric@univie.ac.at

Calcareous nannofossils from the Karpatian - Badenian transition were studied in detail in three Localities (Wagna, Retznei and Perbersdorf) in the Styrian Basin. The co-occurrence of Helicosphaera ampliapereta and Sphenolithus heteromorphus in calcareus nannoplankton assemblages from the "Steierischer Schlier" of the old brickyard Wagna, allows identification of nannoplankton Zone NN4. The nannoplankton Zone NNN4/NN5 boundary is recorded in the upper part of the third profil.

The nannoplankton Zone NN5 was also observed in sediments from the transgressive coral reefs facies on the top of the "Steirischer Schlier" in the cement quarry of Retznei. In Badenian sediments from this locality are identified the following nannoplankton species: Braarudosphaera bigelowii, Coccolithus pelagicus, C. miopelagicus, Cyclicargolithus floridanus, Discoater exilis, D. musicus, D. variabilis, Geminilithella rotula, Helicosphaera carteri, Helicosphaera waltrans, Pontosphaera multipora, Reticulofenestra haqii, R. minuta, Sphenolithus heteromorhus, Sph. moriformis, Umbilicosphaera jafari and Thoracosphaera spp.

The ratio C. pelagicus/R. minuta (calculated as number of C. pelagicus/R. minuta + C. pelagicus x 100) was used for the palaeoenvironmental reconstructions. High values of the Cp/Rm ratio indicate cool-water and high nutrient levels and low values indicate opposite conditions which dominate the interval from the Zone NN4/NN5 boundary upward.

Sediments from borehole Pebersdorf 1 was investigated also and yield rich nannoplankton assamblages.

Biostratigraphic results from the Vienna Basin are based on the drill site for mineral water Vöslau VII. Light brown marls at the top of the basal conglomerate at 240 m, contain a rich nannoflora with frequent Helicosphaera ampliaperta. The accompanying assemblage consist of: Coccolithus pelagicus, Cyclicargolithus floridanus, Disoaster adamanteus, D. druggii, D. exilis, Geminilithella rotula, Helicosphaera carteri, H. euphratis, H. scissura, Pontosphaera multipora, Reticulofenestra haqii, R. minuta, Sphenolithus heteromorphus, Sph. moriformis and Thoracosphaera spp. This level belongs to the nannoplankton Zone NN4 and is correlated with the Early Badenian, Lower Lagenidae Zone.

Samples from 240 m up to 50 m are attributed to the nannoplankton Zone NN5, based on the presence of Sph. heteromorhus in absence of H. ampliaperta. The top of the section belongs to the Agglutinated Foraminifera Assemblage Zone corresponding to nannoplankton Zone NN6.